Virulence factors in multidrug (MDR) and Pan-drug resistant (XDR) Pseudomonas aeruginosa: a cross-sectional study of isolates recovered from ocular infections in a high-incidence setting in southern India

Mesenchymal stem cell-based adjunctive therapy for Pseudomonas aeruginosa-induced keratitis: A proof-of-concept in-vitro study

PURPOSE

Pseudomonas aeruginosa-induced keratitis is one of the most severe and challenging forms of corneal infection, owing to its associated intense inflammatory reactions leading to corneal necrosis and dense corneal scar with loss of vision. Since mesenchymal stem cells (MSCs) are reported to possess antimicrobial and immunomodulatory properties, they can be tested as an adjuvant treatment along with the antibiotics which are the current standard of care. This study aims to investigate the anti-bacterial and immunomodulatory roles of human bone marrow MSC-derived conditioned medium (MSC-CM) in P. aeruginosa-infected human corneal epithelial cells (HCECs) in vitro.

METHODS

The effect of MSC-CM on the growth of clinical isolates of P. aeruginosa was evaluated by colony-forming unit assay. The expression of inflammatory cytokines (IL-6 and TNF-α) and an antimicrobial peptide (Lipocalin 2) in lipopolysaccharide-treated MSCs and HCECs was analyzed through ELISA. Corneal epithelial repair following infection with P. aeruginosa was studied through scratch assay.

RESULTS

Compared to control (P. aeruginosa (5*105) incubated in DMEM (1 ml) at 37 °C for 16 h), MSC-CM significantly: i) inhibits the growth of P. aeruginosa (159*109 vs. 104*109 CFU/ml), ii) accelerates corneal epithelial repair following infection with P. aeruginosa (9% vs. 24% closure of the wounded area after 12 h of infection), and iii) downregulates the lipopolysaccharide-induced expression of IL-6, TNF-α and Lipocalin 2 in HCECs. A combination of MSC-CM with an antibiotic, Ciprofloxacin moderately regulated the expression of IL-6, TNF-α, and Lipocalin 2.

CONCLUSION

MSC-CM holds promise as an adjunctive therapeutic approach for P. aeruginosa-induced corneal epithelial damage.

Chitosan-Loaded Lagenaria siceraria and Thymus vulgaris Potentiate Antibacterial, Antioxidant, and Immunomodulatory Activities against Extensive Drug-Resistant Pseudomonas aeruginosa and Vancomycin-Resistant Staphylococcus aureus: In Vitro and In Vivo Approaches

Antimicrobial resistance poses considerable issues for current clinical care, so the modified use of antimicrobial agents and public health initiatives, coupled with new antimicrobial approaches, may help to minimize the impact of multidrug-resistant (MDR) bacteria in the future. This study aimed to evaluate the antimicrobial, antioxidant, and immunomodulatory activities of Lagenaria siceraria, Thymus vulgaris, and their chitosan nanocomposites against extensive drug-resistant (XDR) Pseudomonas aeruginosa and vancomycin-resistant Staphylococcus aureus (VRSA) using both in vitro and in vivo assays. The in vitro antimicrobial susceptibilities of P. aeruginosa and VRSA strains revealed 100% sensitivity to imipenem (100%). All P. aeruginosa strains were resistant to cefoxitin, cefepime, trimethoprim + sulfamethoxazole, and fosfomycin. However, S. aureus strains showed a full resistance to cefoxitin, amoxicillin, ampicillin, erythromycin, chloramphenicol, and fosfomycin (100% each). Interestingly, all S. aureus strains were vancomycin-resistant (MIC = 32-512 μg/mL), and 90% of P. aeruginosa and S. aureus strains were XDR. The antimicrobial potential of Lagenaria siceraria and Thymus vulgaris nanocomposites with chitosan nanoparticles demonstrated marked inhibitory activities against XDR P. aeruginosa and VRSA strains with inhibition zones' diameters up to 50 mm and MIC values ranging from 0.125 to 1 μg/mL and 1 to 8 μg/mL, respectively. The results of the in vivo approach in male Sprague Dawley rats revealed that infection with P. aeruginosa and S. aureus displayed significant changes in biochemical, hematological, and histopathological findings compared to the negative control group. These values returned to the normal range after treatment by chitosan nanoparticles, either loaded with Lagenaria siceraria or Thymus vulgaris. Real-time quantitative polymerase chain reaction (RT-qPCR) findings presented significant upregulation of the relative expression of the IL10 gene and downregulation of the IFNG gene throughout the experimental period, especially after treatment with chitosan nanoparticles loaded either with Lagenaria siceraria or Thymus vulgaris in comparison to the positive control groups. In conclusion, this is the first report suggesting the use of Lagenaria siceraria and Thymus vulgaris nanocomposites with chitosan nanoparticles as a promising contender for combating XDR P. aeruginosa and VRSA infections as well as a manager for inflammatory situations and oxidative stress-related disorders.

Effect of Age on the Etiology and Antibiotic Susceptibility Pattern of Infectious Endophthalmitis

PURPOSE

To review the etiology and antibiotic susceptibility patterns of infectious endophthalmitis over 11 years in different age groups.

METHODS

Microbiology records of culture-positive endophthalmitis cases from January 2011 and December 2021 were reviewed for the age groups 0-30, 31-60, and >60 years. Additionally, data was also analysed for trends in antibiotic susceptibility between different age groups.

RESULTS

A total of 5590 patients were clinically diagnosed with endophthalmitis. Of these, 1316 (23.5%) patients were culture positive comprising of 1097 bacteria (83.3%) and 219 fungal (16.6%). Gram-positive bacteria predominated the culture-proven bacterial endophthalmitis group with 709 cases (62.6%). Streptococcus pneumoniae (9.3%) was the most prevalent organism in the age group between 0 and 30 years, while Staphylococcus epidermidis (6%) was the most prevalent organism in the age group of 31-60 years. In comparison, Pseudomonas aeruginosa (4.1%) was the most abundant organism in the age group >60 years. Interestingly, Aspergillus flavus (13.24%) was the predominant fungal pathogen in all age groups. There was an increasing trend in antibiotic resistance from younger to older age groups and this pattern was observed for almost all drugs tested except vancomycin and amikacin.

CONCLUSION

While infection can occur at any age, the etiology also seems to vary. This study helps us understand the demography of endophthalmitis along with choice of empirical antibiotics that would influence treatment outcomes. Although vancomycin currently holds good for the treatment for gram-positive infections, gram-negative infections calls for an immediate need for newer drugs or advanced treatment options.

Moving toward Extensively Drug-Resistant: Four-Year Antimicrobial Resistance Trends of Acinetobacter baumannii from the Largest Department of Internal Medicine in Slovakia

A. baumannii imposes a great burden on medical systems worldwide. Surveillance of trends of antibiotic resistance provides a great deal of information needed for antimicrobial stewardship programmes nationwide. Clinical data from long-term, continuous surveillance on trends of antibiotic resistance of A. baumannii in Slovakia is missing. One hundred and forty-nine samples of A. baumannii were isolated over a period of four years. A panel of 19 antibiotics from seven antibiotic categories were tested for the bacterium's susceptibility. Resistance results were evaluated, and the significance of patterns was estimated using simple linear regression analysis. All isolates were more than 85% resistant to at least 13 out of the 19 tested antibiotics. A significant rise in resistance was recorded for aminoglycosides and imipenem from 2019 to 2022. Colistin and ampicillin-sulbactam have been the only antibiotics maintaining more than 80% efficacy on the bacterium to date. A significant rise in extensively drug-resistant (XDR) strains among carbapenem-resistant (CR) isolates has been recorded. Multidrug-resistance (MDR) among all A. baumannii isolates and XDR among CR strains of the bacterium have risen significantly in the last four years.

Comparison of Virulence-Factor-Encoding Genes and Genotype Distribution amongst Clinical Pseudomonas aeruginosa Strains

Pseudomonas aeruginosa is an opportunistic pathogen encoding several virulence factors in its genome, which is well-known for its ability to cause severe and life-threatening infections, particularly among cystic fibrosis patients. The organism is also a major cause of nosocomial infections, mainly affecting patients with immune deficiencies and burn wounds, ventilator-assisted patients, and patients affected by other malignancies. The extensively reported emergence of multidrug-resistant (MDR) P. aeruginosa strains poses additional challenges to the management of infections. The aim of this study was to compare the incidence rates of selected virulence-factor-encoding genes and the genotype distribution amongst clinical multidrug-sensitive (MDS) and MDR P. aeruginosa strains. The study involved 74 MDS and 57 MDR P. aeruginosa strains and the following virulence-factor-encoding genes: lasB, plC H, plC N, exoU, nan1, pilA, and pilB. The genotype distribution, with respect to the antimicrobial susceptibility profiles of the strains, was also analyzed. The lasB and plC N genes were present amongst several P. aeruginosa strains, including all the MDR P. aeruginosa, suggesting that their presence might be used as a marker for diagnostic purposes. A wide variety of genotype distributions were observed among the investigated isolates, with the MDS and MDR strains exhibiting, respectively, 18 and 9 distinct profiles. A higher prevalence of genes determining the virulence factors in the MDR strains was observed in this study, but more research is needed on the prevalence and expression levels of these genes in additional MDR strains.

High-Throughput Transcriptomic Profiling Reveals the Inhibitory Effect of Hydroquinine on Virulence Factors in Pseudomonas aeruginosa

Hydroquinine is an organic alkaloid compound that exhibits antimicrobial activity against several bacterial strains including strains of both drug-sensitive and multidrug-resistant P. aeruginosa. Despite this, the effects of hydroquinine on virulence factors in P. aeruginosa have not yet been characterized. We therefore aimed to uncover the mechanism of P. aeruginosa hydroquinine-sensitivity using high-throughput transcriptomic analysis. We further confirmed whether hydroquinine inhibits specific virulence factors using RT-qPCR and phenotypic analysis. At half the minimum inhibitory concentration (MIC) of hydroquinine (1.250 mg/mL), 254 genes were differentially expressed (97 downregulated and 157 upregulated). We found that flagellar-related genes were downregulated by between −2.93 and −2.18 Log2-fold change. These genes were consistent with the analysis of gene ontology and KEGG pathway. Further validation by RT-qPCR showed that hydroquinine significantly suppressed expression of the flagellar-related genes. By analyzing cellular phenotypes, P. aeruginosa treated with ½MIC of hydroquinine exhibited inhibition of motility (30−54% reduction) and pyocyanin production (~25−27% reduction) and impaired biofilm formation (~57−87% reduction). These findings suggest that hydroquinine possesses anti-virulence factors, through diminishing flagellar, pyocyanin and biofilm formation.

Genetic Identification of Pseudomonas aeruginosa Virulence Genes Associated with Keratitis in Egyptian Population

Infectious keratitis continues to be a prominent cause of vision impairment worldwide through a variety of causes. Pseudomonas aeruginosa is a Gram-negative bacterium that frequently causes vision-threatening microbial keratitis. P. aeruginosa contains a diverse array of virulence factors, including exoA, exoS, nan1, and lasB, some of which may contribute to its pathogenicity. Because the clinical characteristics of bacterial keratitis vary, making a quick differential diagnosis can be difficult, resulting in a delay in diagnosis and worse outcome. In this study, we performed multiplex polymerase chain reaction to detect the presence of nan1, toxA, exoS, and lasB, and determine their association with distinct clinical presentations of P. aeruginosa-related keratitis. We also performed antibiotic susceptibility testing of the isolates. A total of 49 P. aeruginosa strains were obtained from individuals with keratitis between May 2021 and December 2021 from the Research Institute of Ophthalmology, Giza, Egypt. Results showed that lasB was most expressed gene (81.8%), followed by tox (63.6%) and exoS (31.8%), whereas nan1 was the least commonly expressed gene 1316 (22.7%). The antibiotic susceptibility profile showed that TOB was the least sensitive antibiotic (26.5%), followed by CIP (34.7%), whereas CT was the most sensitive antibiotic (89.8%), followed by GAT (83.7%) and PB (81.6%). Several virulence genes were identified in P. aeruginosa isolates, suggesting that these genes are associated with varying degrees of intrinsic virulence and pathogenicity. Substantial associations between specific virulence genes and the source of infection imply that infection control measures can aid in regulating the distribution of virulence genes among P. aeruginosa strains.